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United States Patent |
6,067,728
|
Farmer
,   et al.
|
May 30, 2000
|
Supercritical phase wafer drying/cleaning system
Abstract
An apparatus and method for drying a microelectronic structure on wafer
substrate using supercritical phase gas techniques and a unique pressure
vessel locking mechanism. There is lid and a base with an open cavity to
contain at least one microelectronic structure on wafer substrate.
Clamping the lid to the base uses locking clamp rings with open jaws large
to partially enclose the edge of the vessel. The clamp rings are supported
symmetrically about the sides of the vessel. The rings are adjusted
between an open position where the rings are clear of the vessel and a
locking position where the jaws partially enclose the vessel. The jaws and
the vessel share a tapered cam plate and roller system configured to bring
the rings into vertically compressive locking engagement on the pressure
vessel when the rings are moved into locking position. Mechanical
interlocks provide security against back pressure opening the rings. The
invention includes the necessary mechanisms and systems for manual or
automatic closing and clamping the vessel, controlling pressure in the
cavity, controlling temperature in the cavity, flowing process fluid
through the cavity, venting the cavity, unclamping the pressure vessel,
and removing the lid.
Inventors:
|
Farmer; Robert B. (Billerica, MA);
Jones; Bernard D. (Amherst, NH);
Gupta; Kedar P. (Merrimack, NH);
Jafri; Ijaz H. (Nashua, NH);
Dispensa; Derek M. (Methuen, MA)
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Assignee:
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G.T. Equipment Technologies, Inc. ()
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Appl. No.:
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023290 |
Filed:
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February 13, 1998 |
Current U.S. Class: |
34/470; 34/78; 34/471; 34/476; 134/902 |
Intern'l Class: |
F26B 003/00 |
Field of Search: |
34/467,468,469,470,471,476,73,76,78
134/105,107,108,902
|
References Cited
Other References
Gregory T. Mulhern et al, Supercritical Carbon Dioxide Drying of
Microstructures, pp. 296-300., Seventh International Conference on
Solid-State Sensors & Actuators; Yokohama, Japan, 1993.
John Y. Kim et al, Comparative Study of Various Release Methods For
Polysilicon Surface Micromachining, Jan. 1997, Nagoya, Japan, pp. 442-447.
Dai Kobayashi et al, Photoresist-Assisted Release of Movable
Microstructures, vol. 32, 1993, pp. L1642-L1644, Jpn. J. Appl. Phys.
|
Primary Examiner: Wilson; Pamela A.
Attorney, Agent or Firm: Maine; Vernon C., Asmus; Scott J.
Parent Case Text
This application claims the benefit of U.S. Provisional Application No.
60/040,979 filed Mar. 17, 1997.
Claims
What is claimed is:
1. An apparatus for drying a microelectronic structure on wafer substrate,
comprising
a pressure vessel with a lid and a base with an open cavity, said cavity
being of uniform diameter and constant depth sufficient to contain at
least one said microelectronic structure on wafer substrate, said vessel
when closed comprising said lid emplaced on said base,
means for placing said lid on said base,
means for clamping said lid to said base, said means comprising at least
two locking clamp rings, each said ring having an open jaw sufficiently
large to partially enclose an edge of said vessel when closed, said rings
supported symmetrically about the circumference of said vessel and
oriented with said jaws facing said vessel, said rings movable between an
open position where said rings are clear of said vessel and a locking
position where said jaws partially enclose said vessel, said jaws and said
vessel further comprising a tapered cam plate and roller system configured
to bring said rings into vertically compressive locking engagement on said
pressure vessel when said rings are moved into said locking position,
means for controlling pressure in said cavity,
means for controlling temperature in said cavity,
means for flowing process fluid through said cavity,
means for venting said cavity,
means for unclamping said pressure vessel, and
means for removing said lid from said base.
2. The apparatus of claim 1, said means for clamping said lid to said base
further comprising two locking clamp rings, said jaws configured with
internal upper and lower rollers, said vessel configured with top and
bottom tapered cam plates, said rollers configured to contact respective
said cam plates and bring said rings into vertically compressive locking
engagement on said pressure vessel when said rings are moved into said
locking position.
3. The apparatus of claim 2, further comprising means for rigidly
interconnecting said locking clamp rings when in said locking position.
4. The apparatus of claim 3, said means for rigidly interconnecting
comprising a latching system with mating components secured to respective
locking clamp rings and aligned so as to be brought into connecting
position when said rings are moved into said locking position.
5. The apparatus of claim 4, said means for flowing comprising means for
distributing the incoming flow of said process fluid around the
circumference of said cavity.
6. The apparatus of claim 5, said means for distributing the incoming flow
comprising a system of channels connecting an incoming port to a plurality
of orifices arranged symmetrically about the circumference of said cavity.
7. The apparatus of claim 6, said wafer substrate being fabricated of a
silicon material, said process fluid being carbon dioxide, said means for
controlling temperature being capable of raising and regulating
temperature in said cavity in excess of 30 degrees centigrade, said means
for controlling pressure being capable of raising and regulating pressure
in said cavity in excess of 1000 pounds per square inch over atmosphere.
8. The apparatus of claim 1, further comprising means for automatic
operation according to a pre-determined sequence of process steps and
within manually selectable limits of temperature, pressure and time.
9. The apparatus of claim 8, said means for automatic operation comprising
a computer and control panel interconnected with other said means, said
computer programmed with said predetermined sequence, said computer being
programmable with said manually selectable limits of temperature, pressure
and time.
10. The apparatus of claim 1, further comprising means for automatic
operation according to a pre-determined sequence of process steps and
within pre-determined limits of temperature, pressure and time.
11. The apparatus of claim 1, said means for flowing comprising means for
distributing the incoming flow of said process fluid around the
circumference of said cavity.
12. The apparatus of claim 11, said means for distributing the incoming
flow comprising a system of channels connecting an incoming port to a
plurality of orifices arranged symmetrically about the circumference of
said cavity.
13. An apparatus for drying a microelectronic structure on wafer substrate,
comprising
a pressure vessel with a lid and a base with an open cavity, said cavity
being of uniform diameter and constant depth sufficient to contain a said
microelectronic structure on wafer substrate, said vessel when closed
comprising said lid emplaced on said base,
means for placing said lid on said base,
means for clamping said lid to said base, said means comprising two locking
clamp rings linked by a drive mechanism, each said ring having an open jaw
sufficiently large to partially enclose an edge of said vessel when
closed, said rings slidingly mounted on opposing ends of a common rail
passing beneath said vessel, said rings oriented with said jaws open
towards said vessel, said rings collectively movable by a force on said
drive mechanism between an open position where said rings are clear of
said vessel and a locking position where said jaws partially enclose said
vessel, said jaws configured with internal upper and lower rollers, said
vessel configured with top and bottom tapered cam plates, said rollers
configured to contact respective said cam plates and bring said rings into
vertically compressive locking engagement on said pressure vessel when
said rings are moved into said locking position,
means for controlling pressure in said cavity,
means for controlling temperature in said cavity,
means for flowing process fluid through said cavity,
means for venting said cavity,
means for unclamping said pressure vessel, and
means for removing said lid from said base.
14. The apparatus of claim 13, further comprising
a latching system with mating components secured to respective locking
clamp rings and aligned so as to be brought into latching position when
said rings are moved into said locking position, and
means for actuating said latching system.
15. The apparatus of claim 14, said means for flowing comprising means for
distributing the incoming flow of said process fluid around the
circumference of said cavity.
16. The apparatus of claim 15, said means for distributing the incoming
flow comprising a system of channels connecting an incoming port to a
plurality of orifices arranged symmetrically about the circumference of
said cavity.
17. The apparatus of claim 13, said wafer substrate being fabricated of a
silicon material, said process fluid being carbon dioxide, said means for
controlling temperature being capable of raising and regulating
temperature in excess of 30 degrees centigrade, said means for controlling
pressure being capable of raising and regulating pressure in excess of
1000 pounds per square inch over atmosphere.
18. The apparatus of claim 17, further comprising means for automatic
operation according to a predetermined sequence of process steps.
19. A method for drying a microelectronic structure on wafer substrate,
comprising the steps of:
submerging a said microelectronic structure on wafer substrate in methanol
in a horizontally oriented cavity of uniform diameter and constant
vertical depth in the base of a pressure vessel comprising said base and a
lid,
placing said lid on said base,
clamping said lid to said base with two locking clamp rings, each said ring
having an open jaw sufficiently large to partially enclose an edge of said
vessel, said rings located on opposite sides of said vessel and slidingly
mounted on a common rail system, said rings oriented with said jaws facing
said vessel, said rings interconnected by a drive mechanism and
collectively movable between an open position where said rings are clear
of said vessel and a locking position where said jaws partially enclose
said vessel, said jaws configured with internal upper and lower rollers,
said vessel configured with top and bottom tapered cam plates, said cam
plates oriented with respect to said rollers to bring said rings into
vertically compressive locking engagement on said vessel when said rings
are moved into said locking position,
introducing a through flow of process fluid in said cavity at supercritical
temperature and pressure,
evacuating said process fluid from said closed cavity,
unclamping said lid from said base,
removing said lid from said base, and
removing said microelectronic structure on wafer substrate from said
cavity.
20. The method of claim 19 for drying a microelectronic structure on wafer
substrate, said wafer substrate being fabricated of a silicon material,
said process fluid being carbon dioxide, said supercritical temperature
being in excess of 30 degrees centigrade, said supercritical pressure
being in excess of 1000 pounds per square inch over atmosphere, further
comprising the automatic controlling and sequencing of other said steps.
Description
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to means for the drying of microelectronic wafer
structures so as to avoid surface tension effects, and more particularly
to methods and apparatus for drying silicon wafer microstructures with
supercritical fluids.
2. Background Art
Working to find improvements to the controlled release of microstructures
without subsequent sticking of these structures to the substrate,
researchers at the University of California at Berkeley have developed a
process for drying silicon wafers in a supercritical fluid environment. In
this state, there is no liquid/vapor interface to contribute to the
surface tension effects that cause long, thin microstructures in the order
of 50 micrometers and up, to collapse and stick to the substrate during
the drying process. The supercritical fluid of choice was CO.sub.2, carbon
dioxide, due to it's temperature and pressure thresholds of 31.1 degrees
centigrade and 1073 pounds per square inch over atmosphere.
Using the laboratory method, a silicon wafer containing a pattern of
microelectronic structure, having been fabricated in the conventional
manner, is arranged with a horizontal orientation in a cavity, submerged
in methanol. The cavity is sealed, and a through-flow of liquid carbon
dioxide (CO.sub.2) is introduced for about 15 minutes. The methanol is
rapidly absorbed into the liquid carbon dioxide and carried out of the
cavity. When the cavity has been entirely purged of methanol and is
completely filled with pure liquid carbon dioxide, heat is applied
uniformly for several minutes, causing the carbon dioxide to transition to
it's supercritical phase. It is at this point that the benefit of the
process is realized, as no liquid/vapor interface occurs during this
transition. The CO.sub.2 is then slowly vented to atmosphere, to avoid
turbulence within the cavity.
A vessel that is openable at or near the plane of maximum cross section
area of interior volume, and when closed is subjected to greatly elevated
temperature and pressure, must be of substantial construction, with a
locking mechanism adequate to safely sustain the total pressure applied.
In the university laboratory set up, a circumferential pattern of 8 bolts
is used to secure the lid or top to the base of the vessel, to contain the
high pressure. The subject wafer is placed within the base cavity, the lid
placed in position, the fasteners applied manually to secure the lid, heat
applied to the vessel by external heaters, and ports in the vessel used to
admit and remove the fluids of the process.
There are several obvious problems with the laboratory set up that must be
addressed in order to make this process sufficiently cost-effective and
efficient for use in a production environment. The device is not suitable
for integration into a production line with automated means for inserting
and removing wafers; the closing mechanism is manual and too slow; and the
serially administered steps of the process are manually accomplished and
too slow. The device is also lacking the safeguards required by industrial
standards and regulations for production requirements.
SUMMARY OF THE INVENTION
The invention, in it's simplest form, is an apparatus and method for the
drying of microelectronic structures on wafer substrates using
supercritical phase drying techniques.
It is an object of the invention to provide an apparatus for drying a
microelectronic structure on wafer substrate, consisting of a pressure
vessel with a lid and a base with an open cavity, where the cavity is of
uniform diameter and constant depth sufficient to contain at least one
microelectronic structure on wafer substrate, and the vessel when closed
has the lid emplaced on the base.
The apparatus would include a way for placing the lid on the base, and a
way for clamping the lid to the base using at least two locking clamp
rings linked by a drive mechanism. Each ring would have an open jaw
sufficiently large to partially enclose an edge of the vessel when closed.
The rings would be supported symmetrically about the circumference of the
vessel and oriented with the jaws facing the vessel. The rings would be
collectively movable by a force on the drive mechanism between an open
position where the rings are clear of the vessel and a locking position
where the jaws partially enclose the vessel. The jaws and the vessel would
have a tapered cam plate and roller system configured to bring the rings
into vertically compressive locking engagement on the pressure vessel when
the rings are moved into the locking position.
The apparatus would also have a way for controlling pressure in the cavity,
a way for controlling temperature in the cavity, a way for flowing process
fluid through the cavity, a way for venting the cavity, a way to unclamp
the pressure vessel, and a way to remove the lid from the base.
It is a further object to provide for clamping the lid to the base with two
locking clamp rings, their jaws configured with internal upper and lower
rollers, and the vessel configured with top and bottom tapered cam plates.
The rollers would be configured to contact respective cam plates and bring
the rings into vertically compressive locking engagement on the pressure
vessel when the rings are moved into locking position.
It is a still further object of the invention to provide for automatic
operation according to a predetermined sequence of process steps and
within manually selectable limits of temperature, pressure and time.
It is a yet still further object to provide for automatic operation within
predetermined limits of temperature, pressure and time.
It is another object to provide for rigidly interconnecting the locking
clamp rings when in the locking position, such as with a latching system
with mating components secured to respective locking clamp rings and
aligned so as to be brought into connecting position when the rings are
moved into the locking position.
It is still another object to provide for distributing the incoming flow of
process fluid around the circumference of the cavity, as with a system of
channels connecting an incoming port to several orifices arranged
symmetrically about the circumference of the cavity.
It is yet still another object to provide for the wafer substrate being
fabricated of a silicon material, the process fluid being carbon dioxide,
the raising and regulating of temperature in the cavity in excess of 30
degrees centigrade, and the raising and regulating of pressure in the
cavity in excess of 1000 pounds per square inch over atmosphere.
It is an additional object of the invention to provide a method for drying
a microelectronic structure on wafer substrate, including the steps of
submerging a microelectronic structure on wafer substrate in methanol in a
horizontally oriented cavity of uniform diameter and constant vertical
depth in the base of a pressure vessel that includes a base and a lid,
placing the lid on the base, and clamping the lid to the base with two
locking clamp rings. Each ring would have an open jaw sufficiently large
to partially enclose an edge of the vessel. The rings would be located on
opposite sides of the vessel and be slidingly mounted on a common rail
system with the jaws facing the vessel.
The rings would be interconnected by a drive mechanism and collectively
movable between an open position where the rings are clear of the vessel
and a locking position where the jaws partially enclose said vessel. The
jaws would be configured with internal upper and lower rollers, and the
vessel with top and bottom tapered cam plates, with the cam plates
oriented with respect to the rollers so as to bring the rings into
vertically compressive locking engagement on the vessel when the rings are
moved into locking position.
The method would further include the steps of introducing a through flow of
process fluid in the cavity at supercritical temperature and pressure in a
manner that minimizes turbulence in the methanol as it is being displaced,
then evacuating the process fluid from the closed cavity, unclamping the
lid from the base, removing the lid from the base, and removing the
microelectronic structure on wafer substrate from the cavity.
It is a another additional object of the invention to provide for a method
for drying a microelectronic structure on wafer substrate where the wafer
substrate is fabricated of a silicon material, the process fluid is carbon
dioxide, the supercritical temperature is in excess of 30 degrees
centigrade, the supercritical pressure is in excess of 1000 pounds per
square inch over atmosphere, and there is automatic controlling and
sequencing of other steps.
Still other objects and advantages of the present invention will become
readily apparent to those skilled in this art from the following detailed
description, wherein I have shown and described only a preferred
embodiment of the invention, simply by way of illustration of the best
mode contemplated by me on carrying out my invention. As will be realized,
the invention is capable of other and different embodiments, and its
several details are capable of modifications in various obvious respects,
all without departing from the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Dryer
FIG. 1 is a front elevation of the supercritical fluid dryer, showing the
adjacent water heater/cooler, the control panel, the valve assembly, the
pressure vessel in the closed position, and the clamping mechanism in the
open position.
FIG. 2 is a right side elevation of the supercritical fluid dryer of FIG.
1, with the pressure vessel cover shown in phantom in the open position.
FIG. 3 is a rear elevation of the supercritical fluid dryer of FIG. 1,
showing compressed air and CO.sub.2 inlets.
FIG. 4 is a top view of the supercritical fluid dryer of FIG. 1,
illustrating the layout of the principal components of the clamping
mechanism in the open position surrounding the pressure vessel.
Chamber
FIG. 5 is a top view of the chamber of the pressure vessel of FIG. 1,
showing the lower interior of the cavity of the pressure vessel with a
fluid distribution ring about the circumference.
FIG. 6 is a top view of the fluid distribution ring with variable diameter
holes, as is shown within the chamber of FIG. 5.
FIG. 7 is a front view of the fluid distribution ring of FIG. 6.
FIG. 8 is a left side elevation of the fluid distribution ring of FIG. 6.
FIG. 9 is a side elevation of the chamber of FIG. 5.
FIG. 10 is a rear elevation of the chamber of FIG. 5.
FIG. 11 is the AA cross section view of the chamber of FIG. 10, revealing
it's interior water channels.
FIG. 12 is a bottom view of the chamber of FIGS. 5, 9 and 10, showing the
ports to it's water channels and to the interior cavity of the pressure
vessel, and the mounting holes for the lower roller plates.
Cover
FIG. 13 is a top view of the cover of the pressure vessel of FIG. 1,
showing the ports to it's water channels and the mounting holes for the
upper roller wedges.
FIG. 14 is a left side elevation of the cover of FIG. 13.
FIG. 15 a front elevation of the cover of FIG. 13.
FIG. 16 is the AA section view of the cover of FIG. 14, revealing it's
interior water channels.
FIG. 17 is a bottom view of the cover of FIG. 13, showing the upper surface
of the closed cavity of the pressure vessel of FIG. 1.
Clamp Half Locking Ring
FIG. 18 is a front elevation of the left side clamp half locking ring of
the clamping assembly of FIGS. 1 and 4.
FIG. 19 is a bottom view of the left side clamp half locking ring of FIG.
18, showing the mounting holes for the rail guides.
FIG. 20 is a top view of the left side clamp half locking ring of FIG. 18,
showing the mounting holes for the top plate.
FIG. 21 is an AA sectional view of the locking ring of FIG. 18.
FIG. 22 is a BB sectional view of the locking ring of FIG. 18.
FIG. 23 is a right side elevation of the locking ring of FIG. 18.
Clamping Mechanism
FIG. 24 is a top view of the clamping mechanism of FIG. 4.
FIG. 25 is the AA sectional view of FIG. 24, showing details of the
clamping mechanism.
FIG. 26 is the BB sectional view of FIG. 25, showing the right side spindle
drive gearbox.
FIG. 27 is the CC sectional view of FIG. 25, showing the left side spindle
drive gearbox.
Valve Assembly
FIG. 28 is a top view of the valve assembly of FIG. 1, showing the
mechanical layout of the CO.sub.2 plumbing.
FIG. 29 is front elevation of the valve assembly of FIG. 28.
FIG. 30 is a schematic diagram of CO2 and compressed air systems of the
supercritical fluid dryer.
FIG. 31 is a schematic of the water circulation system of the preferred
embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention is susceptible of many variations. Accordingly, the drawings
and following description of the preferred embodiment are to be regarded
as illustrative in nature, and not as restrictive.
Overview of Structure
Referring to FIGS. 1-4, the relationship of the principal components of the
supercritical fluid dryer is clearly disclosed. The principal components
consist of a water heater/cooler 100 positioned closely to table frame
200, which supports valve assembly 300, pressure vessel 400, clamping
mechanism 500 and control panel 600. The dryer requires the following
inputs: a standard single phase, 115 volt, 40 ampere electrical supply,
0.5 SCFM (standard cubic feet per minute of compressed air at 60-80 PSIG,
and 0.01 cu. ft. (liquid volume) of CO.sub.2 at 1200 PSIG.
Table frame is configured with retractable castors 202, and hood 204. Hood
204 has a transparent viewing panel 206 on the front side, and a blowout
panel 208 on the back side.
Mounted to the back side of table frame 200 is compressed air manual
shutoff valve 331, inline filter 332, pressure regulator 333, and pressure
gauge 334. Also shown are CO.sub.2 supply inlet 301, CO.sub.2 process
outlet 315, CO.sub.2 vent outlet 320, and safety valve outlet 321.
Chamber
Referring to FIGS. 5-12, chamber 420 of pressure vessel 400 of FIG. 1 is
depicted from several views. FIGS. 5, 9 and 10 clearly disclose mating
surface 421 within which is centered chamber cavity 422, a shallow recess
sufficiently large to accept a silicon wafer with supports. O-ring grove
423 in mating surface 421 accepts an O-ring seal for sealing the chamber
to cover 440 (FIGS. 13-17).
Referring to FIGS. 6-8, different views of the fluid distribution ring 700
are shown. The fluid distribution ring structure creates by its profile,
outer circumfrential channels connected by small lateral channels 701 and
703 to the chamber cavity 422. Opposing areas 702, generally coinciding
with fluid inlet and outlet ports (ref. FIG. 12., ports 431 and 432), are
blocked off or void of such channels.
Referring to FIG. 11, the internal interconnected cooling channels 424 are
bored into the chamber from two sides, the entrance holes being then
plugged. Two cooling channel ports 425 through the bottom of chamber 420
into the channels provide inlet and outlet for heating/cooling water
provided from water heater/cooler 100.
Referring to FIG. 12, thermocouple bore 426 accepts a type T thermocouple
436 to provide temperature data on chamber 420. Carbon Dioxide (CO.sub.2)
inlet port 431 and CO.sub.2 outlet port 432 access cavity 422 through the
bottom of chamber 420. The four sets of three hole patterns of support
flange screw holes 435 are provided for mounting support flanges. Eight
sets of three hole patterns of bottom roller plate screw holes 433 are
provided for attach points for eight bottom roller plates 434 (not shown
in this view).
Cover
Referring now to FIGS. 13-17, the cover 440 of pressure vessel 400 is the
same overall diameter as chamber 420 of FIGS. 5-12. Mating flange 441
transitions by tapered shoulder 443 to interior surface 442. This surface
forms the top of cavity 422 of chamber 420 when the cover is placed on the
chamber. Cover 440 has lift assembly attach point 450 centered on it's top
side, and is configured with internal cooling channels 444 and cooling
channel ports 445, similar to the corresponding features of chamber 420.
Eight sets of three hole patterns of locking wedge screw holes 453 are
provided as mounting points for locking wedges 454 (not shown in this
view).
Clamp Half Locking Ring
Referring to FIGS. 18-25 generally, and 18-23 specifically, the left clamp
half locking ring 520 of clamping mechanism 500 is depicted from several
perspectives. Referring to FIGS. 18, 19 and 20, face surface 521
intersects at opposing edges with bottom surface 522 and top surface 523.
FIGS. 21 and 22 show the stepped arrangement of the four upper and four
lower cam follower roller mounting surfaces 524A and 524B respectively.
Cam follower roller mounting surfaces 524A and 524B have cam follower
roller mounting holes 538 through which cam follower roller attach bolts
525 are used to attach cam follower rollers 526. Upper and lower cam
follower roller mounting surfaces 524A and 524B are separated by semi
circular interior surface 539, which accommodates and conforms generally
to the circular shape and height of one side of closed pressure vessel
400.
Top surface 523 has several safety plate screw holes 537. Bottom surface
522 has four hole pattern linear bearing screw holes 527 for linear
bearings 528 (not shown in this view). Back surface 540 has ball screw
attach point 529 from which left clamp half locking ring 520 is pushed and
pulled between the open and clamping positions of clamping mechanism 500.
Clamping Mechanism
Referring to FIGS. 24-27, the layout of clamping mechanism 500, with it's
attendant components is illustrated in detail. FIGS. 22 and 23 show left
and right clamp half locking rings 520 and 550 in the open position, with
cover 440 of pressure vessel 400 in place on chamber 420.
Referring to FIG. 25, two parallel rails 501 are configured to extend left
and right across the bed of table frame 200. Linear bearings 528 are
mounted to the underside of clamp half locking rings 520 and 550, and
slidingly engaged with rails 501.
Referring to FIG. 24, reversible and variable speed drive motor 454 is
connected by shaft coupler 535 to drive train 532 which consists of
several drive shaft elements 533 and two right angle drives 534, to
transfer power to left and right side transmissions 531. Left and right
side transmissions 531 are interlocked by the drive train and configured
to advance and retract screws 530 attached to ball screw attach points 529
on the back surfaces 540 of respective left and right clamp half locking
rings 520 and 550, thereby advancing and retracting the clamp half locking
rings on rails 501 in a synchronous manner towards and away from each
other between open and clamping positions.
Referring to FIG. 25, chamber 420 is configured with support flanges 437 on
its lower surface and supported by support rods 438 secured to table frame
200. Cover 440 shown here in its closed position on top of chamber 420, is
retractable via cover lift assembly 460 (not shown in this figure) to
provide access to the cavity of chamber 420.
With cover 440 in the closed position, drive motor 536 is operable to cause
advancement of clamp half locking rings to a clamping position around
pressure vessel 400, causing left side and right side upper cam follower
rollers 545A and 555A to contact respective locking wedges 454 on cover
440, and left side and right side lower cam follower rollers 545B and 555B
to contact respective bottom roller plates 434 mounted to the bottom of
chamber 420. The advancement of upper cam follower rollers over the 2
degree positive incline of locking wedges 454, opposed by the support of
chamber 420 by lower cam follower rollers against the bottom roller
plates, causes compression and clamping of mating flange 441 of cover 440
against an O ring in grove 423 and the mating surface 421 of chamber 420,
thus sealing chamber cavity 422.
Left and right side safety plates 541 and 551 are bolted to top surfaces
523 of respective left and right clamp half locking rings 520 and 550. The
safety plates are cut out on their respective leading edges so that when
advanced to a clamping position, there is clearance for cover lift
assembly 460. Pneumatically actuated safety latch assemblies 542 are
mounted to either end of left side safety plate 541. Corresponding latch
pin assemblies 552 are mounted to either end of right side safety plate
552 on right clamping half locking ring 550. Latch assemblies 542 are
further configured with latch cams 543 which are engagable with the latch
pin assemblies 552 when the clamp half locking rings are advanced to a
clamping position. Latch pin assemblies 552 are further configured with
plunger actuated pneumatic valves 553, such that the proper engagement of
latch cams 543 with respective pin assemblies 552 operates their plunger
actuated pneumatic valves 553.
Cover Lift Assembly
Referring to FIGS. 2 and 4, cover lift assembly 460 consists of cover lift
arm 461, pivotally connected at one end to cover 440, and at it's other
end to stanchion 462, which in turn is secured to table frame 200. Lift
arm pneumatic cylinder is pivotally attached at one end to table frame 200
and at it's other end to a midpoint on cover lift arm 461, such that full
extension of pneumatic cylinder 463 positions cover 440 on chamber 420,
and full compression lifts cover 440 to the dotted line position of FIG.
2.
Valve Assembly
CO.sub.2 System
Referring to FIGS. 28, 29 and 30, valve assembly 300 with it's associated
parts is illustrated. CO.sub.2 supply inlet 301 (shown on FIG. 3) is
connected serially by high pressure tubing to CO.sub.2 inline filter 302,
pneumatically actuated normally closed CO.sub.2 supply shutoff valve 304,
stepper motor operated CO.sub.2 metering valve 305, metered CO.sub.2
pressure gauge 306, metered CO.sub.2 pressure transducer 307, and hence
through CO.sub.2 inlet 431 into cavity 422 of chamber 420 (shown on FIGS.
11 and 12). A back flow check valve is incorporated at inlet 431.
Cavity 422 (of FIGS. 11 and 12) is further connected via CO.sub.2 outlet
432 serially by high pressure tubing to CO.sub.2 chamber outlet Tee 311,
over pressure safety valve 312, manually operated CO.sub.2 outlet valve
313, pneumatically actuated normally open CO.sub.2 outlet shutoff valve
314, and hence to CO.sub.2 process outlet 315 (shown on FIG. 3). An
adjustable heat jacket 316 covers outlet valve 313 and shutoff valve 314.
Also, CO.sub.2 chamber outlet Tee 311 is further serially connected by
high pressure tubing to pneumatically actuated normally open CO.sub.2 vent
line shutoff valve 317, manually operated CO.sub.2 vent line metering
valve 318, and hence to vent outlet 320 (shown on FIG. 3). Safety valve
312 is further connected to safety valve outlet 321 (shown on FIG. 3).
Compressed Air System
Referring to FIGS. 28, 29 and 30, the compressed air system of the dryer
consists of components connected by pressure tubing as follows: inlet 330
(FIG. 3) to manual shutoff valve 331, to inline filter 332, to pressure
regulator 333, the pressure regulator thus providing regulated air to
pressure switch 334, to lift arm closing solenoid valve 335 and hence to
pneumatic cylinder 463. Regulated air is likewise provided to lift arm
opening solenoid valve 336 and hence to the other end of pneumatic
cylinder 463. Regulated air is likewise provided to safety latch solenoid
valve 337, and hence to both ends of the pneumatic cylinders of safety
latch assemblies 542.
Regulated air is further supplied through serially connected plunger
actuated pneumatic valves 553 of latch pin assemblies 552, to process
section pressure switch 339, to CO.sub.2 supply shutoff solenoid valve 340
and hence to shutoff valve 304, to CO.sub.2 outlet shutoff solenoid valve
341 and hence to shutoff valve 314, and to CO.sub.2 vent line shutoff
solenoid valve 342 and hence to shutoff valve 317.
Water Circulation System
Referring to FIG. 31, the water circulation system of water heater/cooler
100 is illustrated. Water heater/cooler 100 is able to heat or cool water
as necessary to maintain a selected temperature range, and continuously
pump water out outlet 101, to a 3-way solenoid preheat bypass valve 102,
and switchable there from to either pressure side tee 103, hence in
parallel to respective cooling channels of cover 440 and chamber 420,
collecting return water to return side tee 104, passing through a second
3-way solenoid preheat bypass valve 105, and back to inlet 106. Bypass
valves 102 and 105 are connected with a shunt line and operated together
such that water is switchable to be passed through the cover and chamber,
or bypassed through the shunt line. Type T thermocouple 436 mounted in the
center of the underside of chamber 420, provides temperature feedback for
the control function.
Control Panel
Referring now to FIG. 1, control panel 900 integrates control of the
various electrically controllable components with a keyboard/display and
computer capability that provides manual control from the keyboard as well
as programmable semi-automatic sequencing of the functions of the dryer.
Common limit switches and pressure switches are electrically connected to
the control panel are variously placed and adjusted to detect travel
limits of moving components, or pressure levels, for control purposes in
accordance with the overall process.
Operating Cycle
Prior to insertion of a wafer, the pressure vessel is filled with
approximately 30 milliliters of methanol. A wafer is then placed onto a
support structure while keeping a film of methanol on the wafer surface.
The support structure allows an open space above and below the wafer for
unobstructed flow.
The process is then started by pressing the start button on the control
panel. The control panel display will prompt the operator for any
necessary intervention and provide a readout of process status during the
cycle. The cycle commences with the chamber cover being lowered by a
pneumatic cylinder and locking clamps being driven into position by an
electric motor and gear train. This forces cam follower rollers on the
clamps to contact tapered locking wedges on the cover, compressing the
cover to the vessel o-ring seal and creating a sealed and locked assembly.
An electrical limit switch controls the clamp position.
At this point in the cycle, two safety latches located on top of one of the
clamps are pneumatically actuated to provide additional resistance to an
undesired opening due to process pressure. These latches when brought into
position latch onto mounted pins located on the other clamp and contact
two plunger actuated pneumatic valves which in turn allow air pressure to
a bank of solenoid valves. The solenoid valves in turn operate the
CO.sub.2 inlet, dilution and vent shutoff valves making for a fail safe
system because the vessel cannot be pressurized unless the clamps are
closed and the safety latches are locked.
When the above conditions are met the CO.sub.2 inlet valve opens and begins
pressurizing the vessel. The distribution ring in the chamber cavity
inhibits turbulence and promotes a laminar flow of CO.sub.2 around the
subject wafer. The flow rate is controlled by the motor positioning
metering valve. It is important to pressurize the vessel slowly to avoid
turbulence on the product. A transducer mounted in the inlet line senses
pressure and provides a signal to the control panel for set point
comparisons.
When 1100 psi is reached the dilution shutoff valve opens and the CO.sub.2
/methanol mixture begins to dilute out. A manually controlled metering
valve regulates the outlet flow to avoid turbulence in the vessel while
the inlet metering valve is opened further to assure enough pressure to
keep the CO.sub.2 in a liquid state (900 psi minimum). The dilution mode
is controlled by a timed set point (approximately 8 minutes for this
embodiment). At this point the PLC checks for a minimum pressure of 1100
psi and if found to be lower closes only the outlet shutoff valve while
leaving the inlet open. When the set point is satisfied both valves will
be closed and the heating mode will start.
Both the vessel and the cover have channels machined into them for flowing
water for temperature control. A packaged heater/chiller provides the
means for pumping water through the channels and heating the CO.sub.2 to
35-40 deg. Celsius. There is a thermocouple mounted in the vessel
providing a signal to the control panel for set point comparisons.
Preheated water is pumped through the system for approximately 10 minutes
to achieve the temperature noted above. The pressure will undergo a
corresponding rise of approximately 200 psi as the temperature increases
and when the set point temperature is made a supercritical state has been
reached.
The supercritical drying is essentially complete at this point and the
CO.sub.2 needs to be vented for the start of another cycle. A vent circuit
consisting of a shutoff and metering valve similar to the dilution circuit
is also located on the outlet of the vessel. When the heating mode is
complete the shutoff valve opens and performs a controlled vent of the
system. This takes approximately five minutes during which time the
chiller brings the water temperature back under 30 degrees Celsius.
When atmospheric pressure is reached the safety latches are released and
the operator is prompted to press the start button to drive the clamps
open. The clamps open until they contact an electrical limit switch which
stops the drive motor and initiates the opening of the cover. The wafer is
removed and the system is ready for the next cycle.
As will be realized, the invention is capable of other and different
embodiments, and its several details are capable of modifications in
various obvious respects, all without departing from the essence of the
invention.
As an example, the invention includes an apparatus for drying a
microelectronic structure on wafer substrate, which has a pressure vessel
with a lid and a base with an open cavity or bowl or depression formed in
its top surface that is of uniform diameter and constant depth sufficient
to contain at least one microelectronic structure on wafer substrate. A
deeper cavity will hold several wafers in a stacked arrangement. The lid
being emplaced on the base closes the cavity.
The invention includes a mechanism for placing the lid on the base, such as
a pneumatically actuated cylinder that raises and lowers the lid, and has
a way for clamping the lid to the base by using at least two locking clamp
rings, each having an open jaw sufficiently large to partially enclose the
edge of the vessel.
The base of the vessel may be supported on stanchions on a base assembly
and the lid operated by a swinging arm mechanism also attached to the
base. The rings are supported symmetrically about the circumference of the
vessel and oriented with the jaws facing the vessel. The rings are
individually adjusted, or collectively movable by a common drive
mechanism, between an open position where the rings are clear of the
vessel and a locking position where the jaws partially enclose the vessel.
The jaws and the vessel share a tapered cam plate and roller system
configured to bring the rings into vertically compressive locking
engagement on the pressure vessel when the rings are moved into locking
position.
The invention includes the necessary mechanisms and systems for controlling
pressure in the cavity, for controlling temperature in the cavity, for
flowing process fluid through the cavity, for venting the cavity, for
unclamping the pressure vessel, and for removing the lid from the base.
As another example, for clamping the lid to the base, the invention may use
two locking clamp rings, with the jaws configured with internal upper and
lower rollers, and the vessel configured with top and bottom tapered cam
plates, where the rollers are configured to contact respective cam plates
when the rings are moved into locking position, bringing the rings into
vertically compressive locking engagement on the pressure vessel.
As yet another example, the invention includes an apparatus that has a
control panel and control circuits for automatic operation according to a
pre-determined sequence of process steps and within manually selectable or
pre-determined limits of temperature, pressure and time. The apparatus may
have a computer and control panel interconnected with other systems on the
device, where the computer is programmable or programmed with a
predetermined process sequence, and may include pre-determined or
programmable limits of temperature, pressure and time.
As still yet another example, the apparatus may have a way for rigidly
interconnecting or interlocking the locking clamp rings when in the
locking position, such as a latching system with mating components secured
to respective locking clamp rings and aligned so as to be brought into
connecting position when the rings are moved into locking position.
As even still yet another example, the invention includes a pressure vessel
with a way of distributing the incoming flow of process fluid around the
circumference of its cavity, such as a system of channels connecting an
incoming port to a plurality of orifices arranged symmetrically about the
circumference of the cavity.
As another example, the invention includes an apparatus for use with a
wafer substrate being fabricated of silicon material, where the process
fluid is carbon dioxide, the temperature in the cavity can be raised and
regulated at in excess of 30 degrees centigrade, and the pressure in the
cavity can be raised and regulated at in excess of 1000 pounds per square
inch over atmosphere.
As still another example, the invention includes a method for drying a
microelectronic structure on wafer substrate, including the steps of
submerging a microelectronic structure on wafer substrate in methanol in a
horizontally oriented cavity of uniform diameter and constant vertical
depth in the base of a pressure vessel consisting of a base and a lid,
placing the lid on the base, and clamping the lid to the base with two
locking clamp rings. Each ring has an open jaw sufficiently large to
partially enclose an edge of the vessel.
The method may include the base of the vessel being supported on stanchions
on a base assembly and the lid operated by a swinging arm mechanism also
attached to the base. The rings may be slidingly mounted on a common rail
system that may run underneath the base, with the rings positioned on
opposite sides of the vessel and oriented with their jaws open towards the
vessel.
The method would include introducing a through flow of process fluid in the
cavity at supercritical temperature and pressure, evacuating process fluid
from the closed cavity, unclamping the lid from the base, removing the lid
from the base, and removing the microelectronic structure on wafer
substrate from the cavity.
As yet still another example, the method may be for a wafer substrate
fabricated of silicon material, with the process fluid being carbon
dioxide, the supercritical temperature being in excess of 30 degrees
centigrade, the supercritical pressure being in excess of 1000 pounds per
square inch over atmosphere, and further include the automatic controlling
and sequencing of the other steps of the process. The first and last steps
of loading and unloading the wafer from the cavity may be done either
manually or by automated means.
As still yet another example, the process fluid inlet 431 of the chamber of
FIG. 12 may be located in the chamber cover of FIGS. 13-17, so as to
introduce the process fluid from above the methanol bath without
turbulence, rather than up through the bath. The process fluid then
displaces the methanol, which is exhausted through the lower outlet port
432. The distribution ring 700 of FIGS. 5-8, or a similar structure may
likewise be configured in or incorporated with the cover, to disburse the
incoming fluid uniformally and with minimal turbulence.
The objects and advantages of the invention may be further realized and
attained by means of the instrumentalities and combinations particularly
pointed out in the appended claims. Accordingly, the drawing and
description are to be regarded as illustrative in nature, and not as
restrictive.
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